Prior punching machines include revolver punches and TRUMPF® system punches. In revolver punches, the top die tools and bottom die tools are each received in a revolver-like tool holder. Unlike revolver punches, the TRUMPF® system has a gripper system which transports the two tool parts, each for one machining operation, and inserts them into a processing station. The TRUMPF® system can use both punching tools and formation tools. Formation tools can be used to produce reliefs, folds, eyelets, or other shapes in sheet metal workpieces.
The sheet metal workpieces to be processed are moved horizontally on a workbench in what is referred to as a punching stroke plane, so that the workpiece can be positioned properly at the processing station. Deformations are, as a rule, done in an upward direction to prevent the workpiece, upon a motion for subsequent processing operations, from sliding onto what then are downward protrusions instead of sliding onto its flat underside. However, a prerequisite of the upward deformation of the sheet is that in a formation tool, the lower mold insert during a deforming operation remains at a level above the punching stroke plane.
In prior formation tools, a rigid lower mold insert is provided which, in accordance with the deformation to be done, protrudes past the level of the punching stroke plane. In order for the sheet metal workpiece to be transported properly and without damage to the processing station, in conventional formation tools, it is necessary for the stripper plate toward the bottom die, in its initial position, to rest with its top side at the level of the upper edge of the lower mold insert. This means that the sheet metal workpiece, on being transported to the processing position, must be lifted to the level of the lower mold insert via lateral stop chamfers on the stripper plate. In the case of vulnerable surfaces, this can cause processing scratches on the underside of the sheet metal workpiece. In the ensuing deforming operation, the holding-down device of the upper tool insert presses the sheet down laterally of the two aligned mold inserts, so that the desired formation takes place. When the upper or top die tool is lifted again, springs then lift the sheet metal workpiece again and it is moved laterally, whereupon it is again shifted downward onto the punching stroke plane, so that once again there is a risk of damage to the underside of the workpiece.